1. Field of the Invention
The present invention relates to a write once type storage medium represented by DVD (hereinafter referred to as "DVD-R (DVD-Recordable)") having remarkably higher storage capacity than the conventional Compact Disc. More particularly, the present invention relates to an information recording apparatus which reproduces address information or sync information necessary for the position retrieval at the time of recording information, such as video information, and/or reproduces the wobbling signal used for the rotation control of DVD-R (these information and/or signals will generally be referred to in this specification as "pre-information") from the DVD-R on which these information are recorded in advance, so as to record main information such as video and/or audio information.
2. Description of the Prior Art
There is known a CD-R (CD-Recordable) which has the similar storage capacity to CD and is an optical storage medium on which pre-information is recorded in advance and onto which desired main information, such as video and/or audio information, can be recorded based on the pre-information recorded thereon. The pre-information is recorded on the CD-R, at the pre-formatting stage in the manufacturing process, by forming the information tracks (groove tracks or land tracks) wobbled in a wave-like manner at the frequency corresponding to the signal obtained by frequency-modulating the pre-information to be recorded. In recording information onto the CD-R, the wobbling frequency of the wobbled track is detected, and the reference clock for the rotation control of the CD-R is extracted based on the wobbling frequency thus detected. Then, the drive signal for controlling the rotation of the spindle motor is generated on the basis of the reference clock thus extracted, and the clock signal for recording, including the timing signal in synchronism with the rotation of the CD-R, is generated. In order to record address information, indicating the address on the CD-R and necessary for recording main information, the pre-information is reproduced at the time of recording the main information to detect the position where the main information should be recorded.
When recording main information on CD-R, two types of light beams having different intensities are used. The light beam having higher intensity (hereinafter referred to as "recording power") is used to form recording pits, corresponding to the main information to be recorded, on the information tracks, thereby performing recording. The light beam of lower intensity (hereinafter referred to as "reproduction power") is used for the tracking control of the light beam along the information tracks, although its irradiation does not result formation of the recording pits. In CD-R system, the wobbling frequency is sampled to obtain the pre-information only when the light beam of the reproduction power is irradiated. This is because the period of the wobbling frequency is sufficiently longer than the period of the recording pits corresponding to the main information, and hence the pre-information can be successively detected by the sampling performed only when the light beam is at the reproduction power.
However, the above-mentioned DVD-R has a track pitch, between the neighboring information tracks, of approximately half of that of the CD-R, due to the demand of high density recording. Therefore, the wobbling frequency of the neighboring information tracks may interfere with each other if the information track is wobbled to record the pre-information and then the wobbling frequency is sampled to obtain the pre-information in reproduction. As a result, the wobbling frequency may not be correctly detected. For this reason, in DVD-R, the information tracks (e.g., groove tracks) are wobbled at the frequency based on the reference clock, and additionally the pre-information is also recorded on the track located between two neighboring track (e.g., land track) by forming the pre-pits indicative of the pre-information. Further, the pre-pits are formed substantially uniformly over whole surface of the DVD-R so that the reference clock can be reproduced from these pre-pits if necessary.
When recording main information on the DVD-R, it is necessary to use two light beams of different power, i.e., the recording power and the reproduction power, and this is similar to the situation of CD-R. Accordingly, it is required to correctly detect the pre-pits, not only by the light beam of the reproduction power like the case of CD-R, but by the light beam of the recording power, so that the pre-information can be correctly and constantly reproduced from the DVD-R.